In the printing industry, flexographic printing systems are often used as an economical alternative to higher-priced printing systems, such as offset and rotogravure printing. Flexographic printing systems typically include a flexographic printing plate formed from a flat substrate that is deformed and mounted to a printing press cylinder. A raised image may be formed on the printing plate either before or after the printing plate is attached to the printing press cylinder. Unfortunately, such printing systems require a different circumferentially sized printing press cylinder for different final image sizes and further require a separate printing press cylinder and plate assembly for each color to be printed. As one can readily appreciate, large printing plants must stock a large number of printing cylinders to accommodate a wide range of image sizes and colors to be used. With each printing cylinder ranging in price between $100 and $800, the need to stock a large number of printing cylinders can lead to a substantial capital investment.
However, the number of cylinders required can be reduced through the use of interchangeable sleeves that are installed on the printing cylinder. These interchangeable sleeves provide a number of advantages over printing plates, such as providing convenient interchangeability between printing sleeves and printing cylinders. As one skilled in the art will appreciate, sleeve interchangeability reduces the need to stock a plurality of printing cylinders and further reduces the associated capital investment.
In an attempt to vary the circumferential size of the printing plate or sleeves, it is known to apply a rubber covering to the printing cylinder or printing sleeve to thus accommodate various image sizes. This rubber covering is often as much as 0.375″ to 1.00″ thick. Typically, the rubber covering is fabricated directly onto the printing cylinder or fabricated onto a print sleeve, which in turn is mounted to the printing cylinder by known air expansion methods. Unfortunately, these rubber-covered cylinders suffer from a number of disadvantages. In particular, these rubber-covered cylinders require the use of a high temperature vulcanizing process in the manufacture thereof. This process can damage or deform the underlying printing cylinder or print sleeve because of the high temperatures. Furthermore, the vulcanizing process requires cure periods of about a couple hours under pressure to a few days in open air, which adversely effects production throughputs, and finally results in a heavy and cumbersome product that is difficult to handle.
As is known to one skilled in the art, much of the industry is standardized—standard-sized printing cylinders, standard printing pitches (repeats), and standard gear systems. More particularly, much of the industry employs a standard gear system in combination with a standard printing cylinder/printing sleeve circumference to achieve a standard print pitch. Unfortunately, the use of rubber-covered printing cylinders disrupts this standardization in that the rubber covering is added to an existing printing cylinder, thereby changing its circumference and the corresponding print pitch without changing the corresponding gear system. This leads to printing systems that require the use of non-standard, and thus expensive, components.
Flexographic printing systems are often separated into four groups, which include wide web systems, towel and tissue mid web, flexible packaging, folding carton, preprint, and corrugated post print such as those generally between about two feet and ten feet in length, and narrow web systems, such as those generally less than about two feet in length. Wide web systems and narrow web systems differ considerably in that wide web systems do not generally suffer from the same problems as narrow web systems. For instance, it has been common for conventional narrow web flexographic printing systems to suffer from gear marking and impression latitude. Gear marking is a banding of ink in the cross-web direction caused in part by the mechanical interference, such as bounce or chatter, in the gear system driving the narrow web printing cylinder. More particularly, it is believed that this banding is caused from the non-uniform application of pressure from the printing cylinder onto the printing media as the gear teeth enmesh. Wide web systems tend not to be effected as severely by such non-uniform application of pressure, perhaps due to the larger contact surface area available to dissipate such energy.
Still further, conventional narrow web systems traditionally suffer from a lack of impression latitude. Impression latitude is the ability to increase impression without significantly affecting dot gain, slur, color density, reverses, and press speeds, which insures uniform print quality when impression increases due to thickness variation within a plate or cylinder. It is commonly recognized that thicker cushion members (i.e. foam tape) disposed between the printing cylinder and the printing sleeve provide greater impression latitude. However, in conventional narrow web systems there is not typically sufficient area between standard-sized cylinders and standard-sized plates or sleeves to accommodate oversized cushion members. Additionally, such cushion members are relatively expensive and often break down thereby losing their ability to provide any resiliency in narrow web applications.
Still further, the introduction of these cushion members between the printing plates or sleeve and the printing cylinder may cause a variation in the thickness dimension at various points along the outer surface of the printing plate or sleeve. This results in high or low spots in the outer printing surface. This thickness variation is relatively large, typically at least about 0.002 to 0.005″. The prior art rubber coverings also have a limited impression range. Impression range is generally understood as the engagement distance to which the surface of the print substrate can be depressed by the print indicia during the printing operation without causing substantial visible reduction in print performance. For conventional high performance printing, the impression range will not exceed about 0.008″.
Accordingly, there exists a need in the relevant art to provide an enhanced printing press cylinder and method of manufacturing the same that is capable of reducing the effects of gear marking (ink banding) and improving impression latitude. Furthermore, there exists a need in the relevant art to provide an enhanced printing press cylinder and method of manufacturing the same that is capable of overcoming the limitations of conventional systems, such as dot gain, slur, and inconsistency. Still further, there exists a need in the relevant art to provide an enhanced printing press cylinder and method of manufacturing the same that is capable of improving production throughput and reducing production complexity. Lastly, there exists a need in the relevant art to provide an enhanced printing press cylinder and method of manufacturing the same that is capable of overcoming the disadvantages of the prior art.